近年來，兆赫波長光源的應用及產生不論在學術界或是產業界都引起了相當大的注目與關切。其波段包含了由部分毫米波段0.1 THz到遠紅外區10 THz的一段電磁頻譜。目前雖然已有成熟產生兆赫波長光源的技術，但其架構及運轉經費限制了其發展性及普遍性。利用非線性光學原理可產生且有同調性的兆赫波。
本研究以非線性差頻轉換的三波混合之聯立波動方程式，來模擬兆赫波在非線性材料中的消長情形。我們利用程式計算兆赫波的最大轉換效率及其發生時的作用距離(最佳作用距離)，其中包含：(1)兆赫波對不同強度的入射幫浦波之最大轉換效率及最佳作用距離，(2)在固定總入射強度下，兆赫波對不同幫浦波與訊號波比值之最大轉換效率及最佳作用距離。實驗部分利用週期性區域反轉鈮酸鋰質子交換波導來產生同調性的兆赫波。最後探討無法量到有意義之兆赫波訊號的原因。

THz radiation has been extensively explored in recent years due to the great potential in a variety of applications. The THz frequency is typically defined in the range of 100 GHz to 10 THz within the electromagnetic spectrum. The development of THz source is limited by the high of configuration and operation. In this work, we intend to utilize the nonlinear optical approach to generate coherent THz wave.
In this thesis, we simulated the evolution of THz wave in nonlinear crystal by using three coupled wave equations for difference frequency generation (DFG). We analyzed the dependence of THz generation on pump and signal intensities and pump-to-signal intensity ratio. In our simulations, different input intensities or pump-to-signal ratio correspond to different conversion efficiencies and optimal interaction distances. In our experiment, we fabricated an annealed proton exchange-periodic poled LiNbO3 (APE-PPLN) waveguide as the nonlinear conversion crystal. Although there is no measurable THz signal, we analyzed the problems of failure, and provided some solutions in the end.

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